A biennial herb which has naturalized in most temperate regions of the world. It grows vigorously, threatening native plants in meadows and forest gaps. Eradication is extremely difficult since each individual can produce 100,000-175,000 seeds that can remain viable for more than 100 years.

A disease which most commonly affects the endangered green turtle. It causes internal and external tumours which can obstruct crucial functions such as swimming and feeding. First reported in the 1930s in Florida, it is now a pandemic.

With striped grey-green bark this tree is aptly named. It produces dense thickets and has been reported as an aggressive coloniser in acidic forests in Belgium. It has been introduced around the world as an ornamental plant, like so many other invasive species.

Being a comb jelly, this marine species has rows of ‘combs’ (groups of cilia) which it uses for swimming. It is an ‘ecosystem engineer’ which can change water transparency and water nutrient content. It has the impressive ability to regenerate from fragments larger than one-quarter of an individual.

A high-risk, aggressively invasive, strangling fig which is an agricultural weed and “garden thug” – how much worse could it be!? Reportedly invasive to some places where its specialist pollinator wasp has also been introduced. It starts life as an epiphyte, growing on a tree’s surface, before sending its aerial roots down to the ground. The roots end up forming a lattice around the trunk of the host tree which remains after the host tree dies.